The disclosed device herein relates to the field of aeration and mixing of large bodies of fluid. More particularly, the present invention is an improved apparatus for the introduction of gas and dissolved gases into a large body of liquid and for concurrently providing the ability to mix the liquid in a large body of liquid.
Aeration and mixing have been used for treating water and other liquids for more than one hundred years. During that time various devices and methods have been employed for the mixing and aeration of such large bodies of fluid. Such aeration devices include compressor/diffusers, surface aerators, turbine/spargers, jet aerators, blade diffusers, with each having its own utility when it comes to the task at hand.
Compressor/diffuser type aerators employ a compressor suitable to the task to force gas through a diffuser located below the liquid surface. As the bubbles naturally rise to the surface of the liquid being aerated, gas is imparted from the bubbles into the liquid. Resulting mixing of the liquid is provided by the hydraulic resistance of the bubbles as they travel to the liquid surface.
Diffuser type aereators range from coarse bubble to fine bubble diffusers. Coarse bubble systems as the name implies employ larger bubbles and are more reliable but less energy-efficient to operate, when compared to fine bubble systems. Fine bubble diffusing systems, while at first more energy-efficient, frequently become fouled or clogged due to the small apertures required to produce the small bubbles clogging thereby resulting in decreased reliability. Such fine-bubble diffusers, in particular, are limited in low volume capability, due to increased fouling problems at lower gas flow rates.
Compressor diffuser type devices employ a rotating gas diffuser in the form of a large flat horizontal disk-shaped component. Compressed gas is therein discharged from porous plates arranged completely around the circumference of the disk. This type of gas deployment into the liquid tends to produce gas flow where many of the bubbles tend naturally to follow in the path of preceding bubbles which limits the efficiency of the transfer of gas into the surrounding body of liquid. Such a bubble pattern also tends to interrupt the effective inflow of liquid into the reactor column and therefor further limits mixing efficiency. Such a device is shown in U.S. Pat. No. 3,630,498 (Belinski) which teaches the use of a small, high-speed rotating mixing and an aerating element comprising a pair of horizontal radially extending blades or foils. In operation of Belinski, a partial vacuum is formed in a zone of cavitation behind the foils. Gas bubbles which emerge from the blades enter this zone of cavitation and expand due to the reduced pressure around the bubbles. While expanded, the bubbles are shattered by hydraulic forces into smaller bubbles. These smaller bubbles then exit the reduced pressure zone of cavitation and are further reduced in size as they are subjected to ambient pressure. Critical to the Belinski patent is the creation of the zone of cavitation. To create this zone of cavitation in a practical device, the foils must be short (such as 24 inches) and rotated at very high speeds (such as 450 RPM). Consequently, such a device is best suited for a smaller area. If the foils are made appreciably longer, the energy cost and physical loads of high-speed rotation quickly become prohibitive.
Surface aerators employ an engine or motor to rotate impellers or blades near the surface of the liquid body. Such devices conventionally either lift the water into the air above the surface, or aspirate air and inject it just below the surface of the liquid body. Surface aerators in general possess a poor gas transfer efficiency when compared to fine bubble diffused aeration systems since they consume more horsepower hours of energy for each pound of dissolved oxygen they produce. Mixing from surface aerators is generally limited to liquid at or near the surface of the body of fluid being aerated. Further, mixing energy tends to be point limited to positions at or near the impeller. Consequently, localized zones of high shearing forces tend to damage delicate floc structures necessary for proper liquid clarification. Further, surface aerators are generally limited in the length of the shaft overhang, and shaft bearing life tends to be problematic.
Turbine/Spargers aerators use compressors to force and distribute gas below the surface of the liquid body. They also employ a submerged impeller positioned just above the diffuser(sparger), to shear the bubbles and provide bulk mixing of the liquid body in which they reside. Disadvantages of turbine spargers are similar to those for surface aerators with the additional disadvantage caused by the turbine sparger requiring an independent source of compressed gas such as a compressor.
Jet Aerators employ a liquid pump and an eductor to impart gas into the liquid body surrounding them using the Venturi principle. Such a system is taught in U.S. Pat. No. 4,101,286 (Nagao). Such jet aeration systems may also be equipped to mix additional gas, liquid, or solid chemicals into the liquid body into which they are engaged. While such systems are generally reliable and have good low volume capability, they tend to be inefficient aerators.
Blade diffusers as taught in U.S. Pat. No. 1,383,881 (Ingram) use a flotation apparatus having rotating blades which dispense gas bubbles into the surrounding body of liquid. The design of these blades is dictated, however, by the requirement that they also act as impellers to rotate the blades as well as discharging the gas bubbles. Such blades are pitched so that the leading edges are elevated about 45 degrees and as a result, the emerging gas is formed into elongated and then enlarged bubbles, which result in a less efficient introduction of the gas into the liquid. In addition, examination of the patent and our research indicates that the blades would rotate in the opposite direction than is indicated in the Ingram Patent. This would result from the upward flow of fluid caused by the fluid lift pump effect of the released gas moving upward toward the liquid surface. Such a vertical water flow across the pitched blades would appear to in fact cause rotation opposite that which is taught in Ingram.
Another excellent example of a device for aeration and mixing of large bodies of liquid is taught in U. S. Pat. No. 5,681,509 (Bailey). Bailey teaches an apparatus and method for mixing and introducing gas into a large body of liquid by rotating a plurality of permanently mounted spoke-like discharge members which are below the surface of the liquid body. These members have upwardly facing perforated discharge surfaces through which compressed gas is released up into the liquid. Upward lift is countered by angling the members which are tilted with their leading edges lower than their trailing edges and balancing the rotation speed to achieve substantially zero lift. A control system is provided to change the depth of submergence of the discharge members to regulate dissolved gas infusion rate and speed of member rotation to maintain angle of attack. Bailey, while a leader in this field, teaches the use of permanantly mounted blade members which are self supporting for the load forces encountered and which can prove labor intensive to change if needed. Bailey also teaches the use of a vertically inclining main shaft which, while providing valuable utility in the ability to raise the blade members from the liquid in which they rotate, does require a substantial frame and mechanical structure to support the components allowing for the inclining main shaft.
As such, there exists a need for a device for mixing and for introducing gas into a large body of liquid which is easily servicable and energy efficient. Such a device should provide maximum aeration and mixing to the water to which it is immersed and also provide easy ingress and egress of the diffuser blades from the water or liquid being aerated. Such a device should best use diffuser blades that are adaptable for attachment and use with prior systems for aeration to improve on their performance as well as in new installations with frame components designed to further enhance the aeration, energy, and servicing characteristics the device offers. Such a system would best use diffuser blades which are light weight due to transference of loading to load bearing members thereby reducing costs of manufacture and aiding in ease of installation.
The device as herein disclosed features an improved diffuser blade that provides excellent aeration characteristics as well as a highly improved mounting scheme to the rotating hub which provides both compressed gas and rotation to the diffuser blade. The improved mounting system of the diffuser blade enhances both installation of the diffuser blades during the initial installation as well as during removal and reinstallation for maintenance. The improved diffuser blade is mounted on the disclosed support and operating structure and yields maximum utility due to the combined characteristics of the tilting support structure and easily mountable diffuser blades. Or disclosed diffuser blades may also be used to improve currently installed rotational aeration devices if adapted for cooperative installed engagement with aeration systems already in existence to thereby enhance the performance and improve the serviceability of such existing systems.
The disclosed device herein consists of two main components in the form of a support frame which floats upon the liquid and diffuser blades which rotate when immersed in the liquid to aerate the liquid. The frame is mounted upon a means for floatation or continued elevation above a liquid pool such as pontoons or on another means to elevate it above a liquid pool such as a bridge or pier, and provides a platform for a tilting main shaft, a connection to a compressed air source, and a means to rotate a tiltable vertical main shaft such as an electric motor. The frame component features a unique attachment to the main shaft in that the main shaft is rotationally engaged with the frame and can be tilted or cantilevered upward and out of the water or liquid to either mount or service the diffuser blades to the main shaft or during power failures or other times when the diffuser blades need to be raised from the liquid to protect them from clogging.
The diffuser blades attached to the lower or distal end of the main shaft employ a rectangular spar which is cooperatively engaged about its outer surface in a similarly shaped passage formed internally on the diffuser blade. The blade engaging spar is attached in a fixed position about the exterior surface of a mounting tube which either mounts directly to the hub of the main shaft or the mounting tube overlaps a nipple protruding from the hub which is attached to the main shaft. Once engaged for rotation by the main shaft, the mounting tube and spar project substantially normal from the center axis of the main shaft. A pair of cooperatively engageable mounting collars with one affixed on the mounting tube and the other upon the mounting end of the diffuser blade, allow for attachment of the diffuser blade with the mounting tube with the spar engaged with both the exterior of the mounting tube and internally on the diffuser blade. The spar being engaged in a cooperatively engaging passage in the diffuser blade, provides structural support to the diffuser blade during rotation through the fluid and provides support to the diffuser blade in maintaining the angle of attack during rotation in the liquid.
This novel interlocking of the spar with the mounting tube and using a co-operatively engaging passage axially located in the diffuser blade, to engage the diffuser blade upon the spar, allows for easy mounting and dismounting of the diffuser blade to the mounting tube and spar, for both installation and for maintenance or replacement. Further, the provision of the metal spar, which cooperatively engages internally with a passage in the diffuser blade, provides reinforcement to the diffuser blade against the plurality of vector forces imparted upon the diffuser blade when rotating at the determined best angle of attack through the fluid in which it is immersed. This spar and diffuser blade engagement transfers a substantial portion of the vector forces imparted to the diffuser blade including the twisting force and the lateral force imparted to the diffuser blade at the angle of attack during rotation of the main shaft in operative communication with the mounting tube and the nipple. This transfer of force using the spar engaged in the cooperative passage thus allows the diffuser blade itself, and its mounting collar, to be made from much lighter material than if the diffuser blade was required to support the twisting and lateral forces generated by rotating at an angle in the fluid. Further, the current preferred spar engaging the cooperative passage in the diffuser blade has a generally xe2x80x9cuxe2x80x9d shape about it and provides an excellent path for disbursement of compressed gas communicated through the center of the mounting tube up and through the face of the diffuser blade.
The attachment of the diffuser blade engaged over the rectangular shaped spar on the mounting tube, using the mating mounting collars to primarily maintain the diffuser blade upon the spar, also allows for the diffuser blade to be operatively positioned at a determined angle of attack when circulating through the fluid. The desired angle of attack may be achieved using one or a plurality of provided means for rotational engagement of the diffuser blade to the hub. This angle of attack is determined by either first positioning of the spar on the mounting tube in a fixed attachment such that it is at the proper angle to maintain the diffuser blade at the desired angle of attack when inserted thereover, or by taking a mounting tube with an affixed spar thereon, and cooperatively engaging it with the hub with the spar at the correct point to yield the proper angle to an attached diffuser blade. Either means to fix the spar at the proper angle extending from the hub could be used and yield a diffuser blade engaged over the spar with the diffuser blade at the desired angle of attack with the spar absorbing most of the force imparted to the diffuser blade from circulating angled in the fluid.
In order to maximize the shearing effect of the flow of liquid relative to the rotating diffuser blades, it is desirable that the resultant angle of attack of the discharge surfaces of the diffuser blades, with regard to the relative liquid flow, be essentially zero or somewhat greater. In other words, such flow should be generally parallel to or tangential to such surfaces. To achieve this zero angle of attack the illustrated device is designed to take into account the effect of the upward discharge of gas from the diffuser blades. This discharge of gas causes an upward flow of the liquid in a cylindrical or reactor column that is an upward extension of the circle defined by the area between the center axis of the main shaft to the tips of the rotating diffuser blades. Specifically, such discharge of gas produces a zone of liquid above the diffuser blades, which due to the presence of gas bubbles in that liquid, is less dense than the ambient liquid below the diffuser blades. This less dense liquid is displaced vertically upwardly from below by ambient density liquid. The vertical upward flow of the less dense liquid is called the lift pump effect. The ambient liquid that displaces the rising less dense liquid enters the reactor column between the rotating blades. This upward flow of ambient liquid affects the angle of attack between the rotating blades and the ambient liquid.
To achieve the desired zero angle of attack, in view of the aforementioned lift pump effect, the diffuser blades in the current best mode of the device, cooperatively engage through a formed internal passage, with the exterior of the rectangular spar which itself is in registered permanent engagement using welding or attachment components to fix it on the exterior of the mounting tube. Mating mounting attachment collars attached at the proper position to the exterior of the mounting tube and formed at the attachment end of the diffuser blades, hold the diffuser blade from sliding off the supporting spar during rotation in the fluid. The engagement of the internal passage of the diffuser blade over the rectangular spare, which has been properly positioned by affixing it at the correct position on the tube, or by rotating the mounting tube to place the spar in the correct position and then attaching it to the hub, maintains the diffuser blades fixed in a tilted or pitched position with the leading edges of the diffuser blades lowered to a determined angle to yield the zero angle of attack based on a number of factors noted below. The spar as noted must either be attached to the mounting tube at an angle, or rotated with the mounting tube which is then attached to the hub when the spar is properly positioned, such that, when the spar engages with the passage on the interior of the diffuser blade, the zero angle of attack is achieved.
The provision of the easily mounted and dismounted light weight diffuser blade over the spar, and engaged at a determined fixed angle thereon, provides the ability of the diffuser blades to be installed to yield an infinite number of different angles of attack when attached to the mounting tube and adjusted as needed. This angle adjustment is achieved simply by attaching the spar to the mounting tube, by welding or bolting or other means to hold the spar engaged with the mounting tube at the proper determined angle, in such a manner as to yield the desired angle of attack of the diffuser blade when it is cooperatively engaged over the spar. Or as noted, the spar can be affixed to the mounting tube, and then the mounting tube can be attached to the hub with the spar at correct position using a means for engagement of the hub to the mounting tube that will allow for adjustment of the position of the spar before it is fixed to the hub. Changing the angle of engagement of the rectangular spar by either rotating the mounting tube and affixing it to the hub, or by using a mounting tube with the spar positioned properly for a non rotational attachment to the hub, results in a changed angle of attack of the engaged diffuser blade. Of course, in addition to using a means to rotate the mounting tube and then engage it with the hub, the mounting tubes can also be manufactured with the spars attached at different angles to thereby yield the proper angle of attack of the attached diffuser blades. This makes changing the angle of attack of the diffuser blades to the indented purpose easily accomplished by simply changing the mounting tube to one which has the spar attached at the proper angle to engage the diffuser tube and yield the desired angle of attack.
Thus the diffuser blades may be easily manufactured of lightweight material with a properly dimensioned spar engaging passage and attachment collar and be used in a wide variety of liquids and at varying speeds and still yield the proper angle of attack simply by properly attaching the mounting tube to its engagement with the hub to yield the properly angled or positioned spar attached to its exterior. Adjustment of position of the spar to the proper point to engage the diffuser tube interior and hold the diffuser tube at the proper angle of attack is aided by the provision of a hub flange which attaches using fasteners to a mating flange affixed to the mounting tube. The hub flange is provided with a plurality of different hole combinations in the flange which will align with the holes formed in the mating flange to allow the mounting tube, and attached spar to be rotated into the proper position and held in that position by bolts or other fasteners affixed through the properly aligned holes in the hub flange and mating flange. By placing a plurality or large number of different holes in the hub flange, which when aligned with the mating flange will position the spar at varying positions about the center axis running from the hub through the mounting tube, great adjustability for the resulting angle of attack of the diffuser blade is achieved as well as providing substantial structural support to the diffuser blade from the properly positioned spar. Alternatively, these mounting tubes with attached spars could be manufactured in kits with each kit having spars positioned at different angles around the center axis of the mounting tube when attached to the hub directly. While this would eliminate the need for the plurality of different hole mating combinations between the hub flange and mating flange, and is anticipated by this patent, the preferred embodiment employs the hub flange with multiple alignable holes mating to the mating flange because of its adjustability which is especially important during installation and maintenance.
An object of this invention is the provision of an easily mounted and dismounted diffuser blade for rotation in a fluid to both mix the fluid and discharge gas into the fluid from the diffuser blade.
An additional object of this invention is the provision of such a diffuser blade that is light weight due to the provision of an internally engageable spar which reinforces the diffuser blade against rotational and lateral force generated when moving through a liquid.
Another object of this invention is the provision of a diffuser blade that is easily slid upon and engaged over a cooperatively engaging spar which will then maintain the angle of attack of the diffuser blade when rotating in the fluid.
A further object of this invention is to provide a diffuser blade that may be easily changed by slidably engaging the diffuser blade to and from its internal spar engagement.
Yet another object of this invention is the provision of a frame having a main shaft for rotating the diffuser blade in a fluid which may be cantilevered out of the fluid for maintenance or replacement of the diffuser blades.
A further object of this invention is to provide a fail safe system of fluid aeration wherein the diffuser blades aerating the fluid will cantilever out of the fluid should power to the air blower cease, thereby preventing clogging of the diffuser blades.
Yet another object of this invention is to provide a diffuser blade that is slidably mountable to a mounting tube and secured at the proper angle of attack for rotation and being able to change the angle of attack of the diffuser blade by simply changing or rotating the mounting tube in its affixation to the hub to yield a differently angled spar.
These together with other objects and advantages which will become subsequently apparent reside in the details of the construction and operation as more fully hereinafter described and claimed, reference being made to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout.